Figure 2. Induction of enhanced and long-lasting p24-specific immune responses by sPD1-p24_fc vaccination in optimized conditions.

(A) DNA vaccine immunization schedule for BALB/c mice. Mice were immunized at weeks 0, 3, and 6. For assessing overall immune response, mice were sacrificed 2 weeks after the last immunization to collect spleen and blood for analysis of cellular and humoral immune responses. (B) BALB/c mice were immunized with sPD1-p24_fc, sΔPD1-p24_fc, and p24_fc at a dose of 20 μg DNA delivered via i.m./EP. Mice that received PBS only served as negative controls. Two weeks after each vaccination, ELISPOT assays for CD8⁺ T cells and CD4⁺ T cells were performed to test the ability of T cells to produce IFN-γ in specific response to HIV-1 GAG p24 epitopes GAG A-I (CD8) and GAG 26 (CD4), respectively, as well as to (C) IgG1 and IgG2a antibodies specific to HIV-1 p24 in sera detected by ELISA. To determine long-lived immunity, mice were rested for 7.5 months following the immunization regimen before being sacrificed. ELISPOT assays were performed for (D) CD8⁺ T cells and (E) CD4⁺ T cells to test their ability to produce IFN-γ in specific response to HIV-1 GAG p24 epitopes GAG A-I and GAG 26, respectively. (F) Specific IgG1 and IgG2a antibodies against HIV-1 GAG p24 detected by ELISA. Data show the means with standard error from 3 independent immunization experiments with 3 mice per group. *P < 0.05; **P < 0.01.